After running Disk Usage Analyzer on the file system, I am looking for ways to remove unneeded files on my Live USB.

Firstly, is there anything I can do about the files in the casper archive? For example, I noticed that there exists a directory /rofs, which I'm sure stands for read-only file system, the one stored in the read-only casper file, so I can't removing anything in it. Specifically, I removed LibreOffice yet /rofs/usr/lib/libreoffice takes up 222 MB of precious storage, as does Thunderbird and a bunch of other things.

What can I clear regarding the apt program files. /var/lib/apt/lists takes up 115 MB, and /var/cache/apt (not the archives directory) is 139 MB. The /var/cache/apt folder is made up of several ~35 MB files, and I don't know if they are all necessary:

I already clear browsing data regularly when I use chrome, so I don't think I have to deal with that much. However, I see that there are cache folders for other programs, and I wish to know if there is a safe way to remove the cache.

Generally, my question revolves around why I have only less than 300 MB on my 4.0 GB USB thumb drive when I only use it for browsing and simple development in python.

I have persistent storage (casper-rw) and I really just installed chromium, vlc, (I left Firefox on,) I removed big apps like Thunderbird and LibreOffice. I'm thinking that there are unused packages (like libraries) left behind from some of those uninstalls.
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ladaghiniMar 18 '12 at 14:57

2.5GB is the maximum capacity, and like I said, I have like 300MB remaining.
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ladaghiniMar 18 '12 at 15:29

2.5 GB is the maximum capacity, which, as I said earlier, I was reaching. What I would like to know is what is filling up that 2.5 GB (which used to be 2.0, but I added another 512 MB) As far as I am concerned, I have fewer programs installed (space usage wise) than a fresh live USB. And yet, even after adding another 512 MB, I have a measly 300 MB left. There must be some useless files just lurking around.
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ladaghiniMar 19 '12 at 14:59

The files on the iso are read only, you can not delete them. A cow file system makes a copy of the files and tracks the changes, so it takes a lot of space. en.wikipedia.org/wiki/Copy-on-write Again, you need to either remaster the iso or perform a standard installation, but persistence does not work they way you think it does, thus it is not behaving as you expect.
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bodhi.zazenMar 19 '12 at 15:39